Progressive augmentation of locomotor activity in mice by long-term treatment with thyrotropin releasing hormone
Ushijima, I.; Yamada, K.; Noda, Y.; Furukawa, T.
Archives Internationales de Pharmacodynamie et de Therapie 270(1): 29-37
1984
ISSN/ISBN: 0003-9780 PMID: 6437352 Document Number: 226637
The effect of daily administration of thyrotropin releasing hormone (TRH) on exploratory behavior (ambulation) was investigated in mice. TRH administered subcutaneously (2.5 and 10 mg/kg) exerted a biphasic action on locomotion, that is, an increase followed by a subsequent decrease. This TRH-induced hyperlocomotion was inhibited by a small dose of apomorphine (0.25 mg/kg, s.c.), a dopamine receptor agonist, but was conversely increased by a small dose of haloperidol (0.02 mg/kg, s.c.). Following administration of TRH (2.5 mg/kg, s.c.) for 21 successive days, the stimulatory effect on locomotion progressively increased whereas the inhibitory effect decreased, the hyperlocomotion continuing at a later period. At this time, the stimulatory effect of apomorphine (1 mg/kg, s.c.) on locomotion tended to decrease but that of methamphetamine (0.5 mg/kg, s.c.), a catecholamine releaser, was potentiated. The present results suggest that the long-term, daily administration of TRH enhances exploratory behavior of mice, presumably by increasing the synthesis and release of dopamine.